A vibrant seafloor landscape including sponges captured on a Greenpeace expedition earlier this year. (Photo credit: Greenpeace.)
By Rachel Downey (Australia National University & British Antarctic Survey) and Claire Christian (ASOC)
Sponges may historically be one of world’s greatest survivors, but on our planet, we have a number of new human-made challenges that sponges have not come up against before. The deployment of fishing gear that smash seabed habitats, the laying of submarine cables that can destroy tracks of sponge habitat, and oil and gas exploration which can destroy parts or entire sponge habitats. When large numbers of sponges occur together, they are considered indicators of vulnerable marine ecosystems (VMEs), as they likely harbour a rich community of associated animals, like those we often think about in shallow tropical coral reefs, full of brightly coloured fish, worms, crabs and octopus. As the name implies, these areas are sensitive to disturbance and damaging them may have broad ramifications for these ecosystems.
One of the oldest impacts on sponges was sponge fishing, an industry that supplied thousands of tonnes of ‘bath’ sponges for our beauty and industrial needs. Sponge fishing occurred widely in the Mediterranean, but spread globally to encompass the Atlantic and Pacific Oceans. However, overfishing and disease outbreaks destroyed many of these bath sponge grounds in the eighteenth and nineteenth centuries. Bath sponges are now being ‘farmed’ more sustainably, either in the sea by divers and in some areas on ropes, mesh bags, in vitro, or on land-based facilities.
The more recent threat of deep-sea mining for metal-rich nodules has been proposed as a new future hazard to sponges. Vast areas of the deep mid-Pacific Ocean are found to be rich in metal nodules, and on these nodules, completely unique sponges have been found. So far, these new sponges have only been found living on the nodules, rather than on the vast tracts of soft mud that are found throughout deep-sea regions. These nodules are potentially forming ‘biodiversity hot spots’ – localized areas that have a lot of life living on them, like sponges and corals, and their presence means that lots of other animals can use these nodule ‘kingdoms’ to survive, rather than the food-poor mud that surrounds them, a bit like an oasis in a desert.
This red Antarctic sponge is part of a colorful underwater community. (Photo credit: Julian Gutt.)
The scientific community is still unclear about the full impacts of climate change and ocean acidification on sponges. Recent climate change impact studies have given us some idea of how sponges may be ‘winners’ in how they respond to change. In our last post we mentioned that sponges may be able to colonize areas exposed by ice shelf collapse relatively quickly. Research on tropical sponges from the Great Barrier Reef found that some sponges are sensitive to ocean warming, but if oceans simultaneously acidify, then these sponges become less sensitive to temperature increases. Coral bleaching events can also negatively impact sponges directly and indirectly with changes in nutrient cycling, habitat structure, and losses and gains in all the other animals that live among coral reefs. Non-tropical sponges may not be so fortunate either. One recent study showed that more than half of Antarctic species, including sponges, are likely to lose key habitat as sea waters continue to warm in polar regions.
No sponges species are currently threat assessed by the IUCN Red List or protected by the CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora). The IUCN’s Red List, the global authority on the status of threatened species, has begun to recognise the importance in protecting sponges in key environments like the Mediterranean Sea, which will be the first assessment of threats to sponges species in the world.
But it may not be wise to wait for these detailed scientific assessments. Research clearly demonstrates that disturbing seafloor structures has negative ecosystem impacts, and we already know how important sponges are to some of those structures. Bottom-trawl fishing is particularly damaging for the seafloor and can have impacts lasting decades. However, even lower impact methods can disturb sponges and other seafloor dwellers. In Antarctica, for example, longline fishing does result in bycatch. Longline hooks can go as deep as 1000 m and can grab on to sponges, which are often some of the largest parts of the seabed fauna, as the lines are reeled in by fishing vessels. The long-term repercussions of this damage to sponge habitats and associated organisms are not fully known.
To preserve the intricate intra-species relationships and biodiversity that sponges help sustain, we should be proactive and protect VMEs as well as known sponge habitats. Currently, only 3% of the world’s oceans are classified as MPAs (marine protected areas), but only 2% of these are strongly protected. MPAs are located all over the world, not just along countries’ coastlines, like the Great Barrier Reef in Australia and the Channel Islands National Marine Sanctuary in the US, but also in the remote fishing grounds of the high seas, as well as at remote islands, such as the Chagos Marine Protected Area in the Indian Ocean and the Pitcairn Islands in the southern Pacific Ocean.
In the Antarctic, a process is already underway to create a circumpolar network of MPAs around the continent, and the hope is that these MPAs would include seafloor areas representative of Antarctica’s biodiversity. One MPA has already been created in the Ross Sea, one of the largest MPAs in the world, where there are several known large sponge habitats. Another MPA is currently under consideration for the Weddell Sea, which is an area with many vibrant sponge habitats. In the proposed MPA, “ecologically important sponge associations” are singled out for special protection. If the MPA is put in place, no disturbance of these sponge habitats would be allowed, not even for research. Perhaps sponges will get some respect at last.
This Caribbean Pleraplysilla sponge is pretty in pink. (Photo credit, Sven Zea, spongeguide.org.)
Earlier this year, Greenpeace sent one of its ships on an Antarctic expedition in hopes of identifying additional areas to be included in other MPAs. So little is known about these areas that the scientist along on the voyage, Dr. Susanne Lockhart, an expert in Antarctic seafloor species, noted that she’d never seen these species in their natural environment. Usually these areas are only seen with the aid of cameras, and specimens are often gathered using the same equipment for bottom trawling and thus are only examined when dead. Greenpeace employed a two-person submarine, however, enabling Dr. Lockhart to see the species she studied for the first time. She told us:
“Leaving the stark grey-scale world above the ocean in Antarctica, I am always struck by the proliferation of colour and life that can be seen when the submarine reaches the seafloor hundreds of meters below. These densely populated invertebrate communities exhibit a surprisingly high biodiversity and structural complexity that could only have been achieved in the absence of disturbance. Sponges play a key role in that structural complexity; providing habitat and protection for a multitude of other organisms. Such communities have a low resilience to disturbances caused by commercial fishing gear, and are therefore extremely vulnerable and in urgent need of the kind of protection afforded by the Marine Protected Areas proposed for the region.”
Most of us won’t be as lucky as Dr. Lockhart, and will have to admire sponges and the vibrant, complex ecosystems they support from afar, on our TV and computer screens. Meanwhile, we hope you will use your new knowledge about sponges to support comprehensive ocean protection. While protecting one species can often have a broader impact, it’s important to make sure we take a more holistic approach. We still have so much to learn about the interconnections between sponges and their associated organisms – relationships that are likely to have been going on for millennia – as well as how sponges positively impact seabed health, and how they and many other organisms are responding to environmental changes, diseases, and new types of disturbance in the marine environment.
Look closely and you’ll see tiny amphipods using this Antarctic sponge as habitat. (Photo credit: Julian Gutt.)
By Rachel Downey (Australia National University & British Antarctic Survey) and Claire Christian (ASOC)
In our last post, we introduced you to one of nature’s underappreciated animals, the sea sponge. Sponges have been around for over 600 million years, by developing some fascinating adaptations that make them one of our greatest global survivors. Long existence has meant that sponges have been able to colonise the deepest trenches, harshest coastal environments, and survive a multitude of mass extinctions. Today, they live in every marine environment in the world, and even in some brackish and freshwater habitats.
In fact, though sponges with their bright colours and unusual shapes may seem ornamental, they are integral to the functioning of many marine ecosystems. By filtering seawater for food, sponges have a significant impact on water quality, with large sponges able to filter 1500 liters of water per day. Sponges alter the flow of water in their environment, which can be beneficial to other filter-feeding animals, such as brittle stars and sea lilies, which use sponges to get a leg up into the higher food-rich currents.
Furthermore, sponges are never an organism alone, as they host bacteria, viruses, fungi and other marine organisms within their bodies. Sponges are therefore seen as an ecosystem, a big community of lots of organisms, with many different types of relationships, rather than just a single animal. Like trees or corals, sponges are ecosystem engineers, creating complex and varied 3D structures in seafloor habitats that influence the rest of the ecosystem. Many animals, such as fish, scale worms, and brittle stars, rely on sponges as places to feed on their favourite prey, rest, lay eggs, keep their young safe, and occasionally munch on a bit of sponge. Unlike coral reefs, which are restricted to shallow, tropical waters, sponge grounds can occur in every marine environment and at great depth, potentially enhancing biodiversity globally.
An Antarctic fish takes shelter in a sponge. (Photo credit: Tomas Lundalv.)
In coral reef environments, a bacteria that lives in sponge tissue is able to capture phosphorus, making this important nutrient available to the rest of the animals living on the reef. Many of these tropical sponge species contain photosynthesising organisms similar to corals, and these can produce up to three times more oxygen and organic matter than they consume. Thus sponges make substantial contributions to nutrients and oxygen for other animals in the surrounding area. Sponges mainly consume dissolved organic carbon and nutrients that most other marine animals can’t consume. Sponge can consume half their weight in this carbon every day, and instead of using this extra carbon to grow, they shed their old cells, producing food for other organisms. Sponges are great recyclers and providers, keeping themselves and other organisms happy and healthy in many different marine environments.
A sponge’s ability to construct amazing skeletons into innumerable shapes, for their own and other animals’ benefit is also being explored by engineers. These industry researchers are convinced that they can build taller, stronger, and more flexible buildings and vehicles in the future, based on what sponges have mastered over millions of years.
But sponges aren’t simply sitting on the seafloor, waiting to be exploited by other species. They can defend themselves quite well. How do they stay safe on the seafloor? Sponges produce noxious chemicals, often with the help of their bacterial associates, to survive attacks and dominate landscapes. In the last few decades, scientists have been exploring sponge species from every part of the globe to see what unique chemicals they produce. Amazingly, they have found sponges that contain substances that are anti-inflammatory, antibiotic, anti-tumor, vital compounds for our future development in modern medicine, and they can even produce chemicals that are alike to fire retardants! One sponge has been found to contain a bacterium that protects it against arsenic poisoning, which may not sound like an exciting revelation, but this new information could be used to help eliminate our global arsenic poisoning issues, which affects millions of people every day.
In Antarctica, our area of expertise, sponges are an unusually important group. We’re going to focus on them for a bit to further illustrate how critical sponges can be in the polar marine environment. Antarctic sponges live in the shallow, rocky coastal regions that are often scoured clean by icebergs, on the hundreds of isolated seamounts dotted throughout this ocean and on the vast expanses of abyssal, muddy seabed bottoms. The Southern Ocean harbours almost 450 different species from all major sponge groups, including the often brightly coloured and wondrously shaped demosponges, giant spiky vase-like glass sponges, and tiny pale calcareous sponges. Close to half of sponge species that live in this ocean are endemic, meaning that they are not found anywhere else in the world. Antarctic sponges are unusual in that they have very broad longitudinal distributions, so one species can be found around the entire, immense Antarctic coastline and the same species can live in a huge depth range, occurring both in shallow waters and in water hundreds of meters deep. In fact, Antarctic glass sponges are found in shallow marine habitats, a rare phenomenon, as elsewhere in the world they are usually found in very deep waters.
Antarctica is a sponge paradise. (Photo credit: Julian Gutt.)
The relative isolation of the Antarctic region by ocean currents is one reason for this diversity of sponges, since isolation often leads to the evolution of new species. Both abundant silica, necessary for constructing most sponge skeletons, and sea water formed in the deep oceans and then washes up to the shallow coast, may have enabled unusual deep-sea sponges to move from the abyssal depths to the icy coast. The furious Southern Ocean currents circling the continent may have helped distribute sponge larvae all around the Antarctic continent. Whatever the reason, the outcome is clear: Antarctica is a sponge paradise. It has been argued that the biomass (the sheer weight of life) on the Antarctic shelves rivals that of tropical reefs, and this is in part due to the dominance of sponge habitats. By creating complex 3D structures on the seabed, they likely enabled the co-evolution of many Antarctic fish, starfish, crustaceans and much more.
So how did sponges manage to triumph in this harsh polar environment? They are long-lived (some species are thought to be able to live for centuries) and can go for a long time without food, enabling them to survive Antarctic winters when little food will be available and resume growth in the summer when nutrients are more plentiful. Yet patience isn’t the only thing they have going for them. Recent research has revealed that despite their sedentary, slow lives, sponges in Antarctica may be able to move quickly when it counts. After the Larsen A ice shelf collapse, glass sponges moved in very quickly and took over areas newly suitable for life. Soon, other species will likely move in to take advantage of the new habitat these sponges have created.
Furthermore, all sponges produce an incredible array of chemicals to defend themselves and compete for space on the seafloor, and our Antarctic sponges are no exception to this. Only a few sponge species have been studied by pharmaceutical scientists hoping to find compounds to synthesise in their laboratories, and these species have not disappointed, with one species that has compounds that eliminate MRSA, a major source of infection in hospital environments. Some sponges have anti-tumor and anti-viral properties, while others have antibacterial, antimicrobial, and antifungal properties, which are all compounds that can be utilised to improve our fights against human disease.
The Antarctic sponge Dendrilla membranosa contains a substance that could one day be used to treat MRSA. (Photo credit: Bill Baker.)
Unfortunately, Antarctic sponges, as well as those elsewhere in the world, aren’t always allowed to do their habitat engineering and chemical defense creating in peace. In the next post, we’ll talk about the threats to sponges, and why protecting their seafloor habitats should be an important consideration for anyone who loves marine life and appreciates the unique beauty found in our oceans.